ABSTRACT

An experimental study is performed to generate micro-bubbles in the flow passages inside a diamond-shaped cylinder bundle from a pair of tiny holes for supplying air drilled at each of the edge sections between two adjacent cylinders (corresponding to the intersection of the converging- and diverging-flow regions), being induced by the ramming effect. Meanwhile, a flip-flop flow oscillation (a self-excited switching flow phenomenon) is produced at the exit from the cylinder bundle that exhibits multiple, uniform-flow rate jet streams, resulting in a mixed efflux of micro-bubbles and flip-flop flow. Both Coulter Multisizers II and III are employed in monitoring micro-/nano-bubbles in the efflux from the diamond-shaped cylinder bundle. A digital microscopic camera is used for successful visualization photographing of micro-bubbles. Experiments are conducted for the Reynolds numbers ranging from 5000 to 8000 defined based on the flow speed and gap between the edges of two adjacent cylinders as the characteristic velocity and length, respectively. Results are obtained for the number versus diameter of micro-bubbles which are affected by a combined effect of the surface tension, the diameter of tiny holes, and the air supply pressure through the hole, while the Reynolds number plays only a minor role. Most interesting is the occurrence of electrification accompanied by the bursting of micro-bubbles that behave as negative ions. This phenomenon is in accord with electrification accompanying the bursting of bubbles in water and dilute aqueous solutions as reported in the existing literature, which is quoted in the text.
Forced production of micro-bubbles can achieve an efficient supply of oxygen to biological cultivations, enhancement of physiological activity, acceleration of growth of aquamarine, purification of water quality through strengthening micro-biological activity, promoting blood flow in human body, enhancement of chemical reaction, bacteria killing.